This invention relates to ink compositions. More particularly, it relates to water-based ink compositions whose resin component comprises high molecular weight resin acid-maleic anhydride copolymer.
A significant contributor to the print properties of inks is the resin they contain. The resin can influence the gloss, opacity, rub resistance and holdout, among other properties, of the print. Many attempts have been made to develop resins which would impart to inks, including water-based inks, superior levels of gloss, holdout, etc.
In the area of rosin-based resins, it is well-known to modify rosin to improve the print properties of ink formulated therefrom by reacting the rosin at high temperatures with maleic anhydride. The high temperatures promote Diels-Alder and Ene reactions between maleic anhydride and certain resin acids present in the rosin. The reaction products ("rosin maleic anhydride adducts") result from the adduction of one maleic anhydride to one reactable rosin component and are thus of low molecular weight. While such conventional water-soluble-maleic anhydride-modified rosin resins and derivatives thereof are commercially utilized in ink compositions, they often give brittle films that lack scuff resistance and good leveling and tend to dry more slowly than desired.
If instead, a high molecular weight polymer could be formed from components of commercially available rosin, and if this polymer had a higher melting point and better film-toughness than rosin or rosin maleic anhydride adduct, then inks having improved rub resistance, better leveling, faster-drying properties, and thermal and UV stability could be prepared using such polymer. High molecular weight polymers of resin acids present in rosin, and esters thereof, have now been found. They are disclosed and claimed in copending patent application U.S. Ser. No. 191,935, filed on May 9, 1988, the disclosure of which is herein incorporated by reference.